Packaging film and process for preparation thereof



United grates Patent G F PACKAGING FILM AND PROCESS FOR PREPARATION THEREOF Edward Royals Covington and John Warren Meier, Madison, Tenn, assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed July 23, 1957, Ser. No. 673,582

20 Claims. (Cl. 117-445) This invention relates to coating compositions and particularly to coating compositions used to improve the properties of packaging materials.

The necessity of coating regenerated cellulose film, polyethylene terephthalate film, paper and the like to convert them into commercially acceptable packaging materials is well known. The coatings can make the material capable of adhering to itself by the application of heat, termed heat sealing by the art, so that the conversion to bags, containers, etc., is facilitated. The coatings can provide moisture-proofness, a property usually lacking the base material. The coatings can impart printability to a surface that otherwise might display little ability to retain printing inks. The coatings can serve to improve the slip and matting properties of the base material, both properties indicating the ability of the surfaces to slide over each other for easy handling in a wrapping machine. However, no matter which surface property or properties the coating composition serves to improve, it is important that the composition adhere tenaciously to the base material and that the composition does not affect adversely the desirable properties such as flexibility, durability or transparency of the base material.

One or" the most useful group of compositions which fulfills the above requirements are the vinylidene chloride copolymers. However, the level of properties, particularly heat-seal strength, matting and slip, obtained by the use of the vinylidene chloride copolymer compositions heretofore known to the art leave much room for improvement.

it is an object of the present invention to provide a vinylidene chloride copolymer coating composition which produces substantial improvements in the level of packaging fdm properties. It is a further object to provide such a coating composition which will adhere to and improve the properties of a variety of base materials ranging from thermoplastic polymeric materials (polyesters such as polyethylene terephthalate film) to the cellulosic materials (regenerated cellulose film), thus providing new and useful packaging materials. A still further object is to specify a process for preparing the new packaging iflms. Other objects will appear hereinafter.

The objects are accomplished by providing a base film having at least one surface coated with a coating composition comprising essentially a copolymer obtained from 8096 vinylidene chloride, 249.5% of at least one other polymerizable mono-olefim'c monomer copolymerizable therewith, preferably selected from the group consisting or an alkyl acrylate and acrylonitrile, and 0.5-7% of isopropenyl acetate.

Preferably, the coating composition comprises a copolymer obtained from 90-96% vinylidene chloride, 29.5% of at least one ot .er polymerizable mono-olefinic monomer copolymerizable therewith, 0.57% of isopropenyl acetate and 0.52%, based on the combined weight of the previous components, of an unsaturated acidic component selected from the group consisting of maleic an- "ice 2 hydride, acrylic acid, methacrylic acid and itaconic acid.

The invention will be more clearly understood by referring to the descriptive material and the examples which follow. Unless otherwise stated, all parts and percentages given in the examples are by weight. The examples, although illustrating specific embodiments of the present invention, should not be considered limitative.

For convenience, abbreviations will be used in the tables associated with the examples. VCl represents vinylidene chloride; MA, methyl acrylate; IPA, isopropenyl acetate; MAA, methacrylic acid; EHA, 2-ethyl hexyl acrylate; AA, acrylic acid; MAn, maleic anhydride; and AN, acrylonitrile.

EXAMPLE I The coating composition was prepared by adding a dispersing agent, vinylidene chloride, methyl acrylate, isopropenyl acetate, methacrylic acid and water to a vessel fitted with a reflux condenser. The dispersing agent was composed of equal amounts of Duponol WAQ Duponol LS1, and Sulframin ABN After stirring this mixture to disperse the ingredients, a solution of ammonium persulfate and meta-sodium bisulfite in water was added to catalyze the reaction. The mixture was refluxed maintaining the temperature between 32 C. and 36 C. as polymerization progressed. The mixture was stirred until refluxing ceased, thereby indicating the completion'of copolymerization. Upon completion of the reaction, a solution of Duponol LSP was added to stabilize the copolymer against coagulation. The resulting dispersion was cooled and discharged through a filter. The polymeric dispersion was composed of 50% solids. The ingredients used in the preparation are summarized below:

Dispersing agent: Parts Duponol WAQ 1.33 Duponol LSP 1.33 4 Sulframin ABN 1.33

Vinylidene chloride Methyl acrylate 5 isopropenyl acetate 5 Methacrylic acid 5 catalyzing agent:

Ammonium persulfate 0.4} 0 6 Meta-sodium bisulfite 0.2 Stabilizing agent Duponol LSP 1.2 Water 108 The dispersion was then coated on a regenerated cellulose film approximately 0.001" thick which had been pretreated to contain 0.45% of a guanidine-urea-formaldehyde resin obtained by the reaction of guanidine nitrate, formaldehyde and urea as described in Example I of U.S. Patent No. 2,533,557 to Chapman. The coating was applied by passing the film through a coating bath containing the dispersion. Excess dispersion was doctored from the film surface. The coated film was then dried and tested. It had a coating weight, as dried, of 5.9 grams/square meter.

As a control, the regenerated cellulose film was coated in a similar manner with a composition containing all of the above ingredients except the 5 parts of isopropenyl acetate. The coating weight was 5.1 grams/square meter.

1 Sodium lauryl sulfate. 7 2 Sodium oleyl sulfate. 3 Sodium dodecyl benzene sulfonate.

" In the following table, Table 1, the properties of the two films are compared:

Z mu-WA: ""L"-?-Y I bly is placed in an oven maintained at 45 C. Care is exercised to prevent disturbing theuniform alignment of Table 1 Heat seal 7 Film Coating Composition Percent by Strength Shp Matting Anchor- Weight (gum/1.5 age 'Ex.I VCi,/MA/I PA/MAA 90/5/5/0.6 240 Q 1 3 1 -Control VCh/MA/MAA 94.7/5.3/0.5 3 Blocked V 4 details of the methods for testing the films follow: the sheets. The weighted sheets are held in the 45 C.

" Coating weightis determined for cellulosic film by soaking the coated film in a hot solution of a sodium alkyl aryl sulfonate in acetic acid and stripping the coating from the film. The stripped coating in the form of a thin film is dried and weighed. For polyethylene terephthalate base film, coating weight is determined by immersing a portion of the film in cyclohexanone at room temperature for minutes or longer if necessary to dissolve the coating entirely; rinsing in ethyl acetate; and drying overnight at room temperature and 35% relative humidity. The sample is weighed before and after this treatment to determine the coating weight.

Heat-seal strength is measured by cutting a piece of the coated film 4" x 10" with the grain running in the long or machine direction into two pieces 4" x 5" each. The two pieces are superimposed so that opposite surfaces are in contact. The two pieces of superimposed film are then sealed together at each end at right angles to the grain. A A" wide sealing bar heated to a temperature of 125 C. at p.s.i. pressure contacts the ends for second. The sealed sheets are then cut in half at right angles to the grain. From the center of the two resulting pieces, 1 wide strips parallel to the grain are cut. The resulting four sets of strips are tested --by opening each set of strips at the free ends, placing them in a Suter testing machine and pulling them apart. The highest force in grams required to pull the strips apart is taken as a measure of the heat-seal bond strength.

Slip is defined as the resistance or nonresistance of film to shearing action. It is determined by folding the sheet and applying maximum, uniform squeezing pressure on the folded sheet between the thumb and. forefinger and immediately, without releasing the pressure, following this with a slow shearing movement of the thumb and forefinger. The sheets are graded as follows:

Grade 1: The surface slides smoothly over itself. Slip is excellent.

Grade 2: The surfaces slide jerkily over themselves, tending to jump or catch (usually at the beginning of the shearing movement). Slip is fair.

Grade 3: The surface does not slide over itself and the thumb and forefinger tend to slip first. Slip is poor.

Matting is defined as the tendency of a film to adhere.

when two or more surfaces are pressed together; A stack consisting of to 32 3% x 4" sheets of *film, piled back to front throughout the stack is placed on a 3%" x 4" sheet of chipboard and covered with a similar square of chipboard. The assembly is placed on a smooth. sheet of metal at least ,4 thick and approximaterly 6" square. A lead weight with a smooth face (3%" x 4") weighing a total of 4.6 lbs. ($4; lbjper sq. in.) is placed on top of the stack, and the entire assemoven for a of 24 hours. The stacks are then carefully removed from the oven and allowed to cool to room temperature (30 minutes or more). The chipboard is removed and the stack of film sheets is grasped by thumb and forefinger in'the center of the stack. -A shear ing force is thenapplied with care taken to avoid bending'the stack or disturbing its edges, and the sheets are graded as follows:

Grade 1: The sheets slide apart individually with no tendency whatever to cling together.

Grade 1+: The sheets slide apart individually but with perceptible cling.

Grade 2: The stack separates into two or more groups of sheets which remain moderately firmly matted together. V

Grade 2+: The stack separates on application of maximum force into two or more groups of sheets which are firmly matted together.

Grade 3: The stack cannot be separated by straight shearing force and can be separated only by peeling the sheets apart.

Blocked: Matting is so poor that sheets become firmly cemented together and cannot be separated without damaging them.

Anchorage refers to the adhesion of the coating to the base film when in direct contact with Water. Samples of coated film are suspended in water at 45 C. for 16 hours and then graded approximately as follows:

Grade 1-no blisters Grade 2few blisters Grade 3-decided blistering Grade 4-coating sloughs oif at blistered or unblistered V 7 EXAMPLE II A coating composition wasprepared using the monomer's shown in Table 2 and a regenerated cellulose film was coated in a manner similar to that described in Example I with minor changes in'the dispersing and stabilizing agents. The dispersing agent consisted of 1 part each 55' of Sulframin ABN and Duponol =LSP. The stabilizing agent consisted of 1.2 parts of Duponol WAQ and 0.3 part of Daxad 11. The coating weight was 8 grams/ square meter.

It was also attempted to prepare a coating without using isopropenyl acetate. The composition, however, coagulated during reaction and could not be applied to the film.

The composition of the polymer and the properties of the coated film are presented in the following table,

Table 2: V

1 Sodium salt of naphthalene sulfonic acid condensed with formaldehyde.

Table 2 Heat-Seal Film Coating Composition Percent by Weight Strength Slip Matting Anchor- (gms./1.5 age Ex. 11 VCh/MA/AN/EHA/IPA/AA/MAn--, /2. 5/2. 5/2. 512.5/1/1 329 1 1 Control VGlz/MA/AN/EHA/AAIMAD 92. 5/2. 5/2. 5/2. 5/1/1 Coagulated luring reaction EXAMPLE m A coating composition was prepared using the monomers shown in Table 3 and a regenerated cellulose film was coated in a manner similar to that described in Example I with minor changes in the dispersing and stabilizing agents. The dispersing agent consisted of 1 part each of Sulframin ABN and Duponol LSP. The stabilizing agent consisted of 1 part Duponol WAQ, 0.2 part of Daxad l1, and 2 parts of Sulframin ABN. The coating weight was 5 grams/ square meter.

It was also attempted to prepare a coating without using isopropenyl acetate. The composition, however, coagulated during reaction and could not be applied to the film.

mers shown in Table 5 and a regenerated cellulose film was coated in a manner similar to that described in Example I with minor changes in the dispersing and stabilizing agents. The dispersing agent consisted of 1 part each 5 of Sulframin ABN and Duponol LSP. The stabilizing agent consisted of 1.2 parts Duponol WAQ and 0.3 part of Daxad 11. The coating weight was 8.1 grams/square meter.

As a control, the film was coated with a composition prepared in an identical manner except that isopropenyl acetate was omitted. The coating weight was 5.3 grams/ square meter. The polymer compositions and the properties of the coated films are presented in the following table, Table 5:

Table 5 Heat-Sea1 Film Coating Composition Percent by Weight Strength Slip Matting Anchor- S./1.5 age Ex. V V01lluA/AN/EHA/IPA/AA/MAH- 92 2 2 2 2 1 1 Control VCli/MA/AN/EHA/AA/MAn siiziziziiii i i i The composition of the polymer and the properties of EXAMPLE VI the coated film are presented in the following table, Table3:

A coating composition was prepared using the monomers shown in Table 6 and a regenerated cellulose film Table 3 Heat-Seal Film Coating Composition Percent by Weight Strength Slip Matting Anchor- (gum/1.5 age Ex. III VCl /MA/IPA/AA/MAA 90/5/6/025/025 279 2 2 Control VCl /MA/AA/MAA 93.7/5.3/0.25/O.25 Coagulatedcuringreaction.

EXAMPLE IV was coated in a manner similar to that described in A coating composition was prepared using the monomers shown in Table 4 and a regenerated cellulose film was coated in a manner similar to that described in Example I with minor changes in the dispersing and stabilizing agents. The dispersing agent consisted of .66 part each of Dupe-n01 WAQ, Sulfrarnin ABN and Daxad 11. The stabilizing agent consisted of 1 part Duponol WAQ, 2 parts Sulframin ABN and 0.2 part of Daxad 11. The coating weight was 6.2 grams/ square meter.

As a control, regenerated cellulose film was coated with a composition prepared in an identical manner except that isopropenyl acetate wa omitted. The coating weight was Example I with minor changes in the dispersing and stabilizing agents. The dispersing agent consisted of 1 part each of Sulframin ABN and Duponol LSP. The stabilizing agent consisted of 1 part Duponol WAQ, 2 parts Sulframin ABN and 0.2 part of Daxad 11. The coating weight was 5.6 grams/ square meter.

As a control, the film was coated with a composition prepared in an identical manner except that isopropenyl acetate was omitted. The coating weight was 5.0 grams/ square meter. The polymer compositions and the properties of the coated films are presented in the following table, Table 6:

Table 6 Heat-Seal Film Coating Composition Percent by Weight Strength Slip Matting Anchor- (gms./l.5 age VCl /D/IA/AN/EHA/IPA/AA 92/2/2/2/2/1 329 1 1 2 VOl /MA/AN/EHA/AA 94/2/2/2/1 75 2 3 2 4.7 grams/ square meter and the dispersing agent contained EXAMPLE VII 0.66 part Duponol LSP instead of 0.66 part Daxad 11. The polymer compositions and the properties of both A coating composition was prepared using the moncoated films are presented in the following table, Table 4: omers in the ratio shown in Table 7 and a regenerated T able 4 Heat-Seal Film Coating Composition Percent by Weight Strength Slip Matting Anchor- (gms./1.5 age EX. IV VGlz/MA/AN/IPA/MAA 94/3/3/1/1 378 l 2 1 Control VCl /MA/AN/MAA"; 95/3/3/1 l0 3 3 3 EXAMPLE V A coating composition was prepared using the monocellulose film was coated in a manner similar to' that described in Example I with minor changes in the 'dis- 2,950,218 7 8 pe'rsing andstabi-lizing agents. The dispersing agentconpart each of Duponoli WAQfand Duponol LSP be- ;sisted of 66 part, each of, Sulfi'amin ABN, Duponol ing used. The coating weight was 5.1 grams/ square .WAQ and Daxad1l. The stabilizing agent consisted meter;

a of 1 part .Duponol WAQ, 2 parts SulfrarninABN and As a control, the filth was coated with a composi- -0.'2 partof Daxad 11. The coatingweight was 7.2 5 tion prepared in an identical manner except that isograms/squarepmeteri propenyl acetate was .omitted. The coating weight was V As a control, the film was coated with a composition 5.0 grams/square meter. The polymer compositions and prepared in an identical manner except that isopropenyl the properties of the coated films are presented in the acetate was omitted. The coating weight was 6.8 grams/ following table, Table 9:

' Table 9 Percent by Heat- Seal Anchor- Film .Coating Composition Weight Strength Slip Matting age (g'IIlS./1.5i]1.)

Ex. IX VCh/AN/IPA/MAAnn 9o 5 5 o5 261 1 2 1 Control..... VClz/AN/MAA'. game 0.5 o 1 2 2 square meter. The polymer compositions and the proper- EXAMPLE X ties of the coatedfilms are presented in the following 7 table Table 7: 25 A coating composition was prepared using the mon- Table 7 7 I Heat-Seal I Film Coating Composition Percentby Weight Stren th Slip Matting Anchor- 7 (gms.1.5 age Ex. VII VClq/MA/AN/EHA/IPA/MAA-.Q 90/2.5 2.5/2.5/2.5/0.5 245 2 '2 1 Control von MA nN nHA MAA 92.5/2.5/2.5/2.5/0.5 0 2 3 3 i omers shown in Table 10 and a regenerated cellulose EXAMPLE film was coated in a manner similar to that described A coating composition was prepared using the monoin Example I with minor changes in the dispersing and mer's prepared in Table 8 and a regenerated cellulose film 40 stabilizing agents. The dispersing and stabilizing agents was coated in a manner similar to that described in Exconsisted of quantities identical to those mentioned in ample I with' minor changes in the dispersing and st'a- Example VIII above. The coating weight was 7.4 grams/ bilizing agents. The dispersing agent consisted of .66 square meter.

j part each of Sulfr-amin ABN, Duponol .WAQ and As a control, the film was coated with a composition Daxad 11. The stabilizing agent consisted of 1.2 parts a prepared in an identical manner except that isopropenyl each of Dupono WAQ and Daxad 11 and 0.3 part acetate was omitted. The coating weight was 5.6 grams/ of Duponol LSP. The coating weight was 7.4 grams/ square meter. The polymer compositions and the propersquare meter. ties of the coated films are presented in the following As a control, the film was coated with a composition table, Table 10:

Table' 10 V Percent by Heat SeaJ Anchor- Filrn Coating Composition Weight Strength Slip Matting age (gms./1.5 m.)

. Ex. X VClz/lVIA/AN/EHA/IPA/MAA 92/2/2/2/2/1 230 Control.--" VClz/MA/AN/EHA/MAA 94/2/2/2/1 0 prepared in an identical manner except that isopropenyl EXAMPLE XI acetate was omitted. The coating weight was 3.8 grams/ m square meter. The polymer compositions and the P PP A coating composition was prepared using the monties of the coated are PYeSBflted 111 QI O g omers shown in Table 11andapolyethyleneterephthalate table, Table 8: r g V film 0.0005 inch thick was coated in a manner similar to Table 8 Percent by Heat-Seal Anchor- Welght Strength Slip Matting age Film Coating Composition (gms/La in.)

Control..... VOlz/MA/AN/EHA/MAA row EXAMPLE "IX N V A coating composition was prepared usingthe monothat described in Example I and using the same quantimers shown in Table 9 and'a regenerated cellulose film ties of dispersing and stabilizing agents as in Example was rcoated in a manner similar to that described in I. The coating weight was 9.5 grams/square meter. Example I with' only a dispersing agent consisting of 1 7 The composition of the coating polymer and the prop g erties of the coated film are presented in the following table, Table 11.

t where R may be hydrogen, a halogen or a'saturated aliphatic radical and X is selected from one of the fol Table 11 Percent by Heat-Seal Anchor- Film Coating Composition Weight Strength Slip Matting age (gms./1.5in.)

Ex.XI-. VClg/MA/IPA/MAA 90/5/5/0.5 180 1 1 1 EXAMPLE XII lowing groups: Cl, -Br, F, CN, C H

A coating composition was prepared using the monomers shown in Table 12 and glassine paper 0.0012 inch thick was coated in a manner similar to that described 15 y in Example I and using the same quantities of dispersing and stabilizing agents as in Example 1. weight was 6.5 grams/square meter.

The composition of the coating polymer and the properties of the coated film are presented in the following table, Table 12.

The coating Table 12 Percent by Heat-Seal Anchor- Film Coating Composition Weight Strength Slip Matting age (gins/1.5m.)

Ex. XII.-- VCh/MA/IPA/MAA 90/5/5/0. 5 I75 1 1 1 From the foregoing examples it is evident that a wide variety of ingredients may enter the preparation of the films. The films may or may not be resin-impregnated. To obtain increased anchorage at high relative humidities, films sensitive to water vapor may be pretreated with anchoring resins, such as those disclosed in US. Patents 2,159,007, 2,280,829, 2,432,542, 2,533,557, and 2,546,- 575. The films, particularly regenerated cellulose film, may contain softeners or other constituents such as pigments, dyes, delusterants, plasticizers, etc. if desired. The important concept here and the one basic to this invention resides in the use of a critical coating comprising a ccpolymer obtained from 8096% by weight of vinylidene chloride, 249.5% by weight of a polymerizable monomer and 0.5-7 by weight of isopropenyl acetate.

As polymerizable monomers for use with the vinylidene chloride and isopropenyl acetate in the coating, 1 have illustrated the use of alkyl acrylates an acrylonitrile. However, the invention is not limited to these. Any of the following may be used: methyl, ethyl, isobutyl, butyl, acetyl and Z-ethylhexyl acrylates and methacrylates; phenyl methacrylate, cyclohexyl methacrylate, p-cyclohexylphenyl methacrylate, methoxyethyl methacrylate, glycidyl methacrylate, chloroethyl methacrylate, Z-nitro- 2-methyl-propylmethacrylate, and the corresponding esters of acrylic acid; methyl alpha-chloroacrylate, octyl alpha-chloroacrylate, methyl isopropenyl ketone, acrylonitrile, methacrylonitrile, methyl vinyl ketone, vinyl chloride, vinyl acetate, vinyl propionate, vinyl chloroacetate, vinyl bromide, styrene, vinyl naphthalene, ethyl vinyl ether, N-vinyl phthalimide, N-vinyl succinimide, N-vinyl carbazole, methylene diethyl malonate, acrylarnide, methacrylamide or monoalkyl substitution products thereof, phenyl vinyl ketone, diethyl fumarate, diethyl maleate, methylene diethyl malonate, dichlorovinylidene fluoride, dimethyl itaconate, diethyl itaconate, dibutyl itaconate, vinyl pyridine, maleic anhydride, allyl glycidyl ether and other unsaturated aliphatic ethers described in US. Patent 2,160,943. These compounds may be described as vinyl or vinylidene compounds having a single CH C group. The most useful ones fall within the general formula polymers in organic solvents. Unsaturated aliphatic acidic components such as itaconic acid, acrylic acid, methacrylic acid and maleic anhydride are advantageously added to the coating compositions in either aqueous dispersions or organic solutions. However, the acids may be omitted from these compositions with little deleterious effect. It should be pointed out that films coated with compositions that do not include the unsaturated acidic components are inferior in anchorage and adhesion. For this reason, it is preferred to include an unsaturated acidic component in the coating compositions.

The coatings may be applied in accordance with any known coating techniques. They may be applied by passing the film through baths in a continuous manner or in a batch manner. Coatings may also be sprayed onto the film, or applied manually by brushing or the like. The thickness of the coatings may be adjusted in accordance With methods well known in the coating art.

The preferred base material for use in this invention is regenerated cellulose film. Other base materials which may be used in the invention include those shown in Examples XI and XII, polyethylene terephthalate film and paper. Films of cellulose acetate, cellulose propionate, cellulose acetate-butyrate, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, etc. may also be improved by the present invention.

The materials of this invention are used advantageously as packaging materials for foods, cigarettes and the like. They provide flexible, strong materials that, due to improved heat-seal strength, slip and matting, can be easily converted to packages. This coating does not detract from the transparency of the base material and surprisingly, provides excellent non-fogging characteristics. Because of these superior properties the present films are outstanding as a vacuum and pressure packaging material, e.g., for packaging of luncheon meats, cheese, nuts, etc.

As many widely different embodiments can be made without departing from the scope of our invention, it is understood that the invention is not limited except as defined in the appended claims.

Having fully disclosed our invention, we claim:

1. A packaging material comprising a base sheet having at least one surface coated with a composition comprising essentially a copolymer obtained from -96% by weight of vinylidene chloride, 0.5-7% by weight of isopropenyl acetate and 219.5% by weight of at least one other polymerizable mono-olefinic' monomer. copolymerizable with vinylidene chloride selected from the group consisting of 7. A packaging material comprising a base sheet having at least one surface coated'with a composition comprising essentially a copolymer obtained from 90-96% by weight of vinylidenechloride, 0.5-7% by weight of isopropenyl acetate, 2-9.5% by weight of atleast one other polymerizable mono-olefinic monomer copolymerizable with vinylidene chloride selected from the group consisting of alkyl acrylate and acryloni-trile and 0.5-2% based on the combined weight of the previous components, of an unsaturated component selected from the group consisting of maleic anhydride, acrylic acid, methacrylic acid and itaconic acid.

8. A packaging material as in claim 7 wherein the base sheet is a film of regenerated cellulose.

9. A packaging material as in claim 7 wherein the base sheet is a film of polyethylene terephthalate.

10. A packaging material as in claim 7 wherein the polymeriza ble mono-olefinic monomer is acrylonitrile.

11. A packaging material as in claim 7 wherein the polymerizable mono-olefinic monomer is alkyl acrylate. 12. A packaging material as in claim 7 wherein the polymerizable mono-olefinic monomer is methyl acrylate. 13. A process for preparing a packaging film which comprises coasting a base sheet with'an aqueous dispersion containing a copolymer obtainedfrom 80-96% by weight of vinylidene chloride, 0.5-7% by weight of isopropenyl.

acetate and 2-19.5% by weight of at least one other polymerizable mono-olefinic monomer copolymerizable with vinylidene chloride selected from the group consisting of alkyl acrylate and acrylonitrile; and drying the coated base sheet. 7

14.- A process as in claim 13 wherein the base sheet is a film of regenerated cellulose.

15. A process for preparing a packaging film which comprises coating a base sheet with an aqueous dispersion containing a copolymer obtained from 90-9 6% by Weight of vinylidene chloride, 0.5-7% by weight of isopropenyl acetate, 2-9.5 by weight of at least one other 12 polymerizable mo'no-olefinic' monomercopolymeriz able with vinylidene chloride selected from thegroup consisting of alkyl acrylate and acrylonitrile and 0.5-2%, based on the combined weight of the previous components, of an unsaturated component selected from the group consisting of maleic anhydride, acrylic acid, methacrylic acid and itaconic acid; and drying the coated base sheet.

16. A process as in claim 15 wherein the b'asefshet is a film of regenerated cellulose.

l7. Apackaging material comprising a regenerated cellulose film having at least one surface coated with a composition comprisin essentially a copolymer obtained from -96% by weight of vinylidene chloride, 0.5-7% by weight of isopropenylace'tate and 249.5% by weight of methyl acrylate. V p p 18. A packaging material comprising a regenerated cellulose film having atleast one surface coated with a composition comprising essentially a copolymer obtained from 96% by'weight of vinylidene chloride, 0.5-7% by Weight of isopropenyl acetate, 2-9.5% by weight of methyl acrylate. and 0.5-2%, based on the combined Weight of the previous components, of an unsaturated component selected from the group consisting of maleic anhydride, acrylic acid, methacrylic acid and itaconic acid.

19. A process for preparing a packaging film which comprises. coating a regenerated cellulose film with an aqueous dispersion containing a copolymer obtained from 80-96% by weight of vinylidene chloride, 0.5-7% by weight of isopropenyl acetate and 2-l9.5% by weight of methyl acrylate; and drying the coatedfilm.

20. A process for preparing a packaging film which comprises coating a regenerated cellulose film with an aqueous dispersion containing a copolymer obtained from 90-96% by weight of vinylidene chloride, 0.5-7% by weight of isopropenyl acetate, 2-9.5 by weight of methyl acrylate and 0.5-2%, based on the combined weight of the previous components, of an unsaturated component selected from the group consistingof maleic anhydride,

acrylic acid, methacrylic acid and itaconic acid; and drying the coated film.

References Cited in the file of this patent UNITED STATES PATENTS 2,762,720 Michel Sept. 11, 1956 2,829,069 Michel Apr. 1, 1958 2,843,572 Wooten et al. July 15, 1958 v FOREIGN PATENTS- a 654,342 Great Britain June 13, 1951 665,479 Great Britain J an. 23, 1952 

1. A PACKAGING MATERIAL COMPRISING A BASE SHEET HAVING AT LEAST SURFACE COATED WITH A COMPOSITION COMPRISING ESSENTIALLY A COPOLYMER OBTAINED FROM 80-96% BY WEIGHT OF VINYLIDENE CHLORIDE, 0.5-7% BY WEIGHT OF ISOPROPENYL ACETRATE AND 2-19.5% BY WEIGHT OF AT LEAST ONE OTHER POLYMERIZABLE MONO-OLEFINIC MONOMER COPOLYMERIZABLE WITH VINYLIDENE CHLORIDE SELECTED FROM THE GROUP CONSISTING OF ALKYL ACRYLATE AND ACRYLONITRILE. 